1. Field of the Invention
The invention relates in general to a semiconductor structure and method for manufacturing the same, and more particularly to a SCR (silicon controlled rectifier) electrostatic discharge (ESD) structure for protecting an internal integrated circuit and method for manufacturing the same.
2. Description of the Related Art
Electrostatic Discharge (ESD) Protection devices have been widely used in CMOS circuits to protect the internal circuit from damage due to the electrostatic discharge. FIG. 1 is a cross-sectional view of a conventional ESD protection device, which is formed by P+/N-well junction. Also, FIG. 1 shows a basic ESD device demonstrated by a diode. The diode is disposed between the pad and the internal circuit to prevent the internal circuit from the damage caused by the electrostatic discharge flowing through the pad to the internal circuit. The P+/N-well junction forms a diode and is disposed between the pad and the internal circuit. The internal circuit, for example, can be a VLSI (very large scale integration) circuit. The P+/N-well junction is usually used as a ESD protection device in the integrated circuit (IC) manufactured by CMOS (complementary metal-oxide-semiconductor) process. As shown in FIG. 1, the semiconductor structure for protecting an internal integrated circuit includes a P-type substrate (doped with P-type ions) 100, a N-well 110 formed in the P type substrate 100, a P+ doping region 116 connected to the pad in the N-well 110 to form a ESD protection device, a diode 112, and a N+ doping region 114 in the N-well 110 connected to the voltage source (Vcc). Moreover, a P+ doping region 116 in the P-type substrate 100 is connected to the ground. The conventional ESD protection device is usually disposed between the internal circuit and pad for protecting the internal circuit from burning due to the electrostatic discharge damage.
However, the ESD protection device is not suitable to be applied in high voltage CMOS process due to the propagation characteristics of conducting wire and a large dimension of general ESD devices. The current flowing through the ESD devices is not uniform, which may affect the electrical characteristics, such as breakdown voltage, of the ESD device. Besides, in high voltage CMOS process, the diode ESD device usually accompanies with one ground which also shares the same ground with the internal circuit. The high voltage ESD device may suffer high voltage such as 400 volts; thus, if the ground of the ESD device shares with the low voltage (such as 5 volts) internal circuit, the electrical characteristics of the internal circuit may be affected due to the ground not be fixed at zero volts, especially when the internal circuit is an analog integrated circuit.